The present invention relates generally to diagnostic imaging and, more particularly, to a CT detector array having uniform cross-talk. More particularly, the invention is directed to a CT array constructed such that the optical cross-talk through the reflector between CT detectors is purposely increased so as to offset reduced electrical cross-talk and coupler layer cross-talk typically present at the interface of CT detectors. Increasing the cross-talk through the reflector between adjacent CT detectors reduces cross-talk discontinuities that contribute to artifact presence in a final reconstructed diagnostic image.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage.
Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
“Cross-talk” between detector cells of a CT detector is common. “Cross-talk” is generally defined as the communication of data between adjacent cells of a CT detector. Generally, cross-talk is sought to be reduced as cross-talk leads to artifact presence in the final reconstructed CT image and contributes to poor spatial resolution. Typically, four different types of cross-talk may result within a single CT detector. X-ray cross-talk may occur due to x-ray scattering between scintillator cells. Optical cross-talk may occur through the transmission of light through the reflectors that surround the scintillators. Known CT detectors utilize a contiguous optical coupling layer(s), typically epoxy, to secure the scintillator array to the photodiode array. Cross-talk, however, can occur as light from one cell is passed to another through the contiguous layer. Electrical cross-talk can occur from unwanted communication between photodiodes.
Cross-talk between adjacent elements of a CT detector is relatively uniform throughout the single CT detector. However, at the junction of one CT detector to another, there is generally a drop in cross-talk. The drop in cross-talk results from increased reflector material and anti-cross-talk matter disposed between CT detectors or modules as well as reduced electrical cross-talk and coupler layer cross-talk customarily present at the interface or boundaries of adjacent CT detectors. While cross-talk reduction is generally preferred between elements of single CT detector, a drop of cross-talk between CT detectors results in cross-talk discontinuities throughout the CT detector array. These discontinuities negatively affect the final reconstructed image.
Additionally, backlit photodiodes are commonly being used in CT detectors. Backlit diodes are particularly susceptible to electronic cross-talk. As a result, at the interface or junction of CT detectors, there is a greater discontinuity in cross-talk as backlit photodiodes intrinsically are discontinuous in cross-talk at the boundaries of adjacent CT detectors. The implementation of backlit photodiodes, however, is preferred as backlit photodiodes have better tileability and improved interconnectivity than traditional photodiodes.
CT detector array construction typically results in a greater reflector thickness between CT detectors than that found between detector elements of the CT detector. This results in a very finite space that limits the amount of scintillator surface area. If the junction between CT detectors was constructed to match or be less than the width between detector elements of a single CT detector, more of the array space can be devoted to scintillator surface area thereby improving x-ray detection. Additionally, reducing the thickness of reflector material disposed between CT detectors provides improved module to module tolerances for detector manufacturability.
Therefore, it would be desirable to design a CT detector array having uniform cross-talk so as to reduce discontinuities typically found at the interface of adjacent CT detectors. It would also be desirable to design a CT detector array with reduced reflector width between CT detectors thereby improving manufacturing and detector element placement.